2. Field of the Invention
The present invention relates generally to a ceramic electronic component, and more particularly, to an improvement in an electronic component having plating films formed on electrodes exposed to its outer surfaces so as to enhance solderability and corrosion resistance.
2. Description of the Prior Art
Examples of ceramic electronic components include a ceramic electronic component having wiring electrodes formed on at least one of its major surfaces and terminal electrodes and the like formed on its side surfaces, for example, a ceramic multilayer substrate. Another example is an alumina substrate for an IC package having electrodes formed on its one major surface and its side surfaces.
The ceramic electronic component having the electrodes on both the major surface and the side surfaces as described above is superior in balance of conductivity, costs and the like and has a relatively high melting point. Accordingly, in the ceramic electronic component, Ag or an Ag-Pd alloy is often used as a material constituting the electrodes. However, Ag or an Ag system alloy is eroded by solder, so that corrosion resistance of the electrodes is insufficient.
Consequently, in the ceramic electronic component using Ag or an Ag system alloy as a material constituting the electrodes exposed to its outer surfaces, the corrosion resistance of the outer electrodes must be enhanced.
Therefore, an attempt to coat the surfaces of the outer electrodes with another conductive material by plating to enhance corrosion resistance of the outer electrodes has been conventionally made. For example, as a ceramic substrate on which a transistor is mounted, a ceramic substrate having plating films made of Au formed on wiring electrodes on its major surface on which the transistor is mounted and plating films made of low-cost Sn formed on electrodes on its side surfaces has been proposed.
Furthermore, as an IC package, an IC package in which overgraze layers are formed on wiring electrodes exposed to the exterior and then, plating films made of Au are formed thereon has been used. Also in the case, plating films made of an Ni-Sn alloy and solder are formed on terminal electrodes.
In the conventional ceramic electronic component having wiring electrodes, terminal electrodes and the like on both its major surface and its side surfaces as described above, plating films are formed on the electrodes so as to enhance corrosion resistance of the electrodes. However, the electrodes formed on the major surface and the electrodes formed on the side surfaces are coated with plating films made of different materials, so that the plating film forming process must be carried out several times, which is very complicated.